1. Field of the Invention
The present invention relates to metallized moisture vapor permeable sheets having an inorganic surface layer to prevent corrosion of the metal layer.
2. Description of the Related Art
It is known in the art to use moisture vapor permeable (breathable) metallized sheets as house wrap in building construction. The metallized sheets allow moisture vapor to pass through the sheet, thus preventing moisture condensation in insulation that is installed behind the sheet, while at the same time providing a barrier to air and liquid water and enhancing the energy efficiency of the building. U.S. Pat. No. 4,999,222 to Jones et al. describes moisture vapor permeable metallized polyethylene sheets with low emissivity prepared by calendering a plexifilamentary film-fibril sheet followed by vacuum metallization. U.S. Pat. No. 4,974,382 to Avellanet describes an infiltration and energy barrier that can be vapor permeable or impermeable having at least one metallized layer thereon. Published PCT International Application No. WO 01/28770 to Squires et al. describes breathable building membranes that include an under layer of microporous film and a top layer formed of a filamentous polymeric fabric, for example a spunbond fabric, which is provided with a moisture vapor permeable reflective metal coating. While the breathable metallized sheets described above provide a thermal barrier by reflecting infrared radiation, they are susceptible to oxidation of the metal layer upon exposure to air and moisture. An oxidized metal layer generally has a higher emissivity than the corresponding metal and is less effective as a thermal barrier. In addition, a thin exposed metal layer can be damaged during processing, installation, etc.
Published European Patent Application No. EP 1400348 to Avril et al. describes liquid impermeable, moisture vapor/gas permeable laminated fabrics that are suitable for use as construction fabrics such as house wrap and roofing underlay that include a reflective film layer formed by vapor depositing a metal layer on a first polymeric film layer and sandwiching the metal layer between the first polymeric film layer and a second polymeric film layer. The film layers protect the metal layer from damage during use, but are moisture impermeable and are microperforated after metallization to provide the desired moisture vapor permeability.
Metallized nonwovens that have been coated with an organic polymer are also known for construction end uses, such as house wrap. However, the polymeric coating is applied using methods that significantly reduce the moisture vapor permeability compared to the uncoated metallized nonwoven sheet. U.S. Patent Application Publication No. 2003/0136078 to Brown et al. describes a method of insulating a building that includes the step of introducing an insulating membrane comprising a reflective layer and a breathable textile layer into the cavity between the outer cladding layer and the frame. The metallized layer may optionally be coated with a protective layer of plastic or varnish to protect the metal surface.
When a moisture vapor permeable sheet is coated over substantially an entire surface using conventional methods such as air knife coating, flexographic printing, gravure coating, etc., the coating reduces the moisture vapor permeability of the sheet. If the starting sheet has an open structure and is highly air permeable, the sheet can retain sufficient moisture vapor permeability after coating to be useful in certain end uses, such as apparel. For example, fabrics described in U.S. Pat. No. 5,955,175 to Culler are both air permeable and moisture vapor permeable after being metallized and coated with an oleophobic coating. However, when the starting moisture vapor permeable sheet has a highly closed structure with very low air permeability, such as nonwoven and other sheets used as house wrap or roof lining in the construction industry, conventional coatings result in significant covering of the pores on the surface of the sheet. This results in a coated sheet having significantly lower moisture vapor permeability than the starting sheet. This is undesirable in house wrap and roof lining products, which are desirably permeable to moisture vapor while at the same time forming a barrier to infiltration by air and liquid water. This process also results in a coated sheet with a substantially higher emissivity than the uncoated metal layer.
US Patent Application Publication US 2004/0213918 A1 (Mikhael et al.) discloses a process for functionalizing a porous substrate, such as a nonwoven fabric or paper, with a layer of polymer, and optionally a layer of metal or ceramic. According to one embodiment, the process includes the steps of flash evaporating a monomer having a desired functionality in a vacuum chamber to produce a vapor, condensing the vapor on the porous substrate to produce a film of the monomer on the porous substrate, curing the film to produce a functionalized polymeric layer on the porous substrate, vacuum depositing an inorganic layer over the polymer layer, and flash evaporating and condensing a second film of monomer on the inorganic layer and curing the second film to produce a second polymeric layer on the inorganic layer. Mikhael et al. also discloses another embodiment including the steps of flash evaporating and condensing a first film of monomer on the porous substrate to produce a first film of the monomer on the porous substrate, curing the film to produce a functionalized polymeric layer on the porous substrate, vacuum depositing a metal layer over the polymer layer, and flash evaporating and condensing a second film of monomer on the metal layer and curing the second film to produce a second polymeric layer on the metal layer.
It would be desirable to provide metallized sheets that have good protection against oxidation while not sacrificing high moisture vapor permeability and good thermal barrier properties for construction uses such as house wrap and roof lining, and other uses requiring good thermal barrier properties such as clothing and tents.